There is a deep rooted belief that eating yogurt decreases the risk of vaginal yeast infections from taking broad spectrum antibiotics. This is not an effective strategy. Antibiotics are absorbed through the intestinal tract and are distributed throughout our bodies through the bloodstream. They kill unfriendly bacteria but unfortunately also friendly bacteria, like the normal vaginal flora.
The magic of yogurt is that it contains bacteria that are very similar to the bacteria that normally live in the vagina and keep its environment a little acidic, which deters yeast from growing.
But if anybody thinks yogurt bacteria are absorbed in the intestinal canal and transported throughout or bodies via the bloodstream to the vagina, they are wrong. Such a scenario would basically amount to sepsis, blood poisoning.
However, a little dab of yogurt inside the vagina is the simple, practical way of letting the vaginal flora’s cousins “house sit” until a woman’s own friendly bacteria have a chance to recover from the antibiotic treatment they were subjected to because of a urinary infection or whatever else her medical provider prescribed it for.
That’s how it really works.
A Country Doctor Writes: 
Yes, I have lectured this information to undergraduate students at Ohio University taking my Human Biology Course for the past 20 years. I would add that organic yoghurt with live lactobacilli be used not cheaper products.
I know I’ve seen research articles showing oral probiotics could colonize the vagina, but this article from Harvard says most of those studies are poorly designed: https://www.health.harvard.edu/blog/should-you-use-probiotics-for-your-vagina-2019122718592
So…this is interesting. I can eat all the yogurt and pop all the probiotics I want and it still won’t help vaginal yeast? I have heard of inserting a probiotic capsule into the vaginal, and the yogurt as well, but I was not aware that consuming it was ineffective.
Always learning!
Laurie
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Thank you!
I’m an FNP working in women’s health for years. I’ve taking to explaining to my patients that humans are like “very complicated donuts” with the GI tract being the donut hole. While some things are absorbed in the gut, other things (like probiotics) just pass through the donut hole. But the number of Gyn providers who recommend PO probiotics for vaginal flora health always leaves me questioning.